The invention relates generally to generating X-rays and specifically to a method and system for generating monochromatic X-rays.
X-ray imaging systems are generally utilized for various applications in the medical and non-medical fields. For example, medical X-ray imaging systems, such as radiographic systems, computed tomography (CT) systems, and tomosynthesis systems, are used to create internal images or views of a patient. Based on the attenuation of the X-rays and on the type and amount of data acquired, different views may be constructed, including views showing motion, contrast enhancement, volume reconstructions, two-dimensional images and so forth. Alternatively, X-ray imaging systems may also be utilized to in non-medical applications, such as in industrial quality control or in security screening of passengers, packages, and/or baggage. In such applications, acquired data and/or generated images or volumes may be used to detect objects, shapes or irregularities which are otherwise hidden from casual visual inspection and which are of interest to the screener.
Typically, X-ray imaging systems, both medical and non-medical, utilize X-ray tubes to generate the X-rays used in the imaging process. Often, conventional X-ray tubes emit a broad spectrum of X-rays, i.e., X-rays at a broad range of wavelengths, which may be detrimental and/or inefficient for a particular X-ray imaging procedure. For example, depending on the attenuation properties of the material being imaged, a particular dose, or quantity, of X-rays at a particular wavelength may be desired for generating the desired image data. Because a conventional X-ray tube typically emits X-rays not only at the desired wavelength but also at other wavelengths, conventional X-ray tubes may inadvertently increase the X-ray dosage received by the subject.
For example, some medical X-ray imaging procedures, such as angiography, employ a contrast agent, which is substantially opaque to X-rays of a given wavelength. The contrast agent is introduced into a particular artery or vein and images are captured which reveal the shape of the artery or the vein and which can help to diagnose an obstruction, blockage, or narrowing. Because the contrast agent is maximally opaque within narrow range of X-ray wavelengths, it is only necessary to employ X-rays within this range to achieve a good contrast to noise ratio (CNR), i.e., high quality image. A conventional X-ray tube however, emits X-rays not only in the desired narrow range but also at other wavelengths outside the narrow range, thereby subjecting the subject to a higher dose of X-rays than is necessary to obtain the desired image data. Likewise, other imaging techniques, both medical and non-medical, typically rely primarily on X-rays within a narrow range of wavelengths which interact suitably with the material of interest, such as bone, metal, etc. X-rays outside the narrow range of interest add little to the image quality.
Currently, selection of a suitable X-ray generation technique (such as the power of the electron beam and/or the composition of the target material) and filtration of the resulting broad spectrum of X-rays are used to control the wavelengths of X-rays generated and reaching the subject. These techniques, however, increase the size and weight of the X-ray source and are relatively expensive to implement. Furthermore, existing techniques for controlling X-ray spectral characteristics may be difficult to adjust to generate different X-ray spectra or particular, X-ray wavelengths.
Thus there exist a need for a method and system to easily generate X-rays having a narrow range of wavelengths. In particular, there is a need for a method and system for generating monochromatic X-rays having substantially the same wavelength.